1. Field of the Invention
The present invention generally relates to systems and methods for irradiation and more particularly to homogeneous radiation distribution systems and methods.
2. Description of Related Art
Radiation therapy (also known as radiotherapy, radiosurgery or radiation oncology) is the medical use of ionizing radiation as part of cancer treatment to control malignant cells. Radiotherapy is used for the treatment of malignant tumors (cancer), and may be used as the primary therapy. It is also common to combine radiotherapy with surgery, chemotherapy, hormone therapy or some mixture of the three. Most common cancer types can be treated with radiotherapy in some way.
Radiotherapy may be used for different purposes, including curative or adjuvant cancer treatment. Radiotherapy is often used as palliative treatment (i.e., where cure is not possible and the aim is provide local disease control or symptomatic relief) or as therapeutic treatment (i.e., where the therapy has survival benefit and it can be curative). The precise treatment intent (e.g., curative, adjuvant, neoadjuvant, therapeutic, or palliative) will depend on the tumor type, location, and stage, as well as the general health of the patient.
Radiotherapy may include various techniques, such as Total body irradiation (TBI) which is used to prepare the body to receive a bone marrow transplant. Radiotherapy also has several applications in non-malignant conditions, such as the treatment of trigeminal neuralgia, severe thyroid eye disease, pterygium, pigmented villonodular synovitis, prevention of keloid scar growth, and prevention of heterotopic ossification. The use of radiotherapy in non-malignant conditions is limited partly by worries about the risk of radiation-induced cancers.
The amount of radiation used in radiation therapy is typically measured in gray (Gy), and varies depending on the type and stage of cancer being treated. For curative cases, the typical dose for a solid epithelial tumor ranges from 60 to 80 Gy, while lymphoma tumors are treated with 20 to 40 Gy. Preventative (adjuvant) doses are typically around 45-60 Gy in 1.8-2 Gy fractions (e.g., for breast, head and neck cancers). Many other factors are considered by radiation oncologists when selecting a dose, including whether the patient is receiving chemotherapy, whether radiation therapy is being administered before or after surgery, and the degree of success of surgery.
The total dose may be fractionated (spread out over time) for several important reasons. Fractionation allows normal cells time to recover, while tumor cells are generally less efficient in repair between fractions. Fractionation also allows tumor cells that were in a relatively radio-resistant phase of the cell cycle during one treatment to cycle into a sensitive phase of the cycle before the next fraction is given. Similarly, tumor cells that were chronically or acutely hypoxic (and therefore more radioresistant) may reoxygenate between fractions, improving the tumor cell kill.
Irradiation is the process by which an item is exposed to radiation. In common usage the term refers specifically to ionizing radiation, and to a controlled level of radiation that will serve that specific purpose, such as radiation therapy, rather than radiation exposure to normal levels of background radiation or abnormal levels of radiation due to accidental exposure.
During radiation therapy, it is desirable to provide the most effective dose to the treatment area (e.g., a tumor) while limiting any radiation exposure to healthy cells. Radiotherapy is commonly applied to the cancerous tumor and it is necessary to subject a margin of normal tissue around the tumor to radiation to allow for uncertainties in set-up and internal tumor motion. These uncertainties can be caused by internal movement (e.g., respiration and bladder filling) and movement of external skin marks relative to the tumor position. To spare normal tissues (e.g., skin or organs which radiation must pass through in order to treat the tumor), shaped radiation beams are aimed from several angles of exposure to intersect at the tumor, providing a much larger absorbed dose at the tumor than in the surrounding, healthy tissue. One technique for example includes the use of a gamma knife. A gamma knife device contains 201 cobalt-60 substantially fixed sources of approximately 30 curies (1.1 TBq) each, placed in a circular array in a heavily shielded assembly. The device aims gamma radiation through a target point in the patient's brain. The patient wears a specialized helmet that is surgically fixed to their skull such that the brain tumor remains stationary at target point of the gamma rays. An ablative dose of radiation is thereby sent through the tumor in one treatment session, while surrounding brain tissues are subject to reduced levels of radiation. Unfortunately, the gamma knife may still subject certain areas of normal tissue to increased radiation levels.
Accordingly, it is desirable to provide a technique for the irradiation to a treatment area while lowering the effective levels of irradiation of non-treatment areas, thereby treating the affected area while limiting damage to adjacent tissue.